1. Field of the Invention
The present invention relates to an image forming system and an image forming apparatus.
2. Description of the Related Art
Conventionally, there is known a tandem-type image forming system in which two image forming apparatuses are connected in series. According to the tandem-type image forming system, in double-sided printing, for example, the first image forming apparatus performs printing on the front side of a sheet, and the second image forming apparatus performs printing on the backside of the sheet. Since the first image forming apparatus and the second image forming apparatus partially take responsibility in double-sided printing, as compared with an image forming system in which one image forming apparatus performs double-sided printing alone, the productivity can be increased. In general, such a tandem-type image forming system is applied to a PP (Production Print) machine which pursues high productivity.
Japanese Patent Application Laid-open Publication No. 2005-22243 discloses that, in an image forming system in which two image forming apparatus are connected in series, a paper ejection apparatus is provided between the first image forming apparatus and the second image forming apparatus. By providing the paper ejection apparatus between the two image forming apparatuses, sheets can be ejected to their respective destinations depending on which of double-sided printing and single-sided printing is performed on each of the sheets. Accordingly, the sheets undergoing double-sided printing and the sheets undergoing single-sided printing are not ejected to one paper ejection tray so as to be mixed therein.
Furthermore, Japanese Patent Application Laid-open Publication No. hei 10-86455 discloses that, in an image forming system in which two image forming apparatus are connected in series, a sheet bypass or an escape path (sheet storage path) is provided in the second image forming apparatus. By providing the sheet bypass, sheets can be carried at high speed in single-sided printing. In addition, by providing the sheet storage path, when the first image forming apparatus is broken or a jam occurs therein, the second image forming apparatus can continue printing in such a way that the order of documents is not changed from their original order.
Here, a case is examined, the case where single-sided printing is performed in a tandem-type image forming system, and the first image forming apparatus thereof performs single-sided printing.
According to Japanese Patent Application Laid-open Publication No. 2005-22243, the sheets on which single-sided printing is performed by the first image forming apparatus are ejected to the paper ejection apparatus provided between the first image forming apparatus and the second image forming apparatus. Consequently, it is not necessary to drive the second image forming apparatus. Accordingly, components/materials (photosensitive drums and developing solutions) of the second image forming apparatus can be prevented from deteriorating or being consumed. However, the paper ejection apparatus is provided between the first image forming apparatus and the second image forming apparatus, and another paper ejection apparatus is provided at a downstream side of the second image forming apparatus, and hence a large space is required for the overall system.
Furthermore, according to Japanese Patent Application Laid-open Publication No. hei 10-86455, the sheets on which single-sided printing is performed by the first image forming apparatus are carried to the sheet bypass in the second image forming apparatus. Consequently, it is not necessary to drive materials (photosensitive drums and a developing device) of the second image forming apparatus. Accordingly, the materials thereof can be prevented from deteriorating. However, the sheet bypass is provided in the second image forming apparatus, and hence the costs for the second image forming apparatus increase.
That is, the tandem-type image forming systems disclosed in Japanese Patent Application Laid-open Publications No. 2005-22243 and No. hei 10-86455 raise problems of the space increase (increase in size) or the cost increase when only single-sided printing is taken into consideration. A preferable image forming system is an image forming system having a configuration to which the configuration of a conventional tandem-type image forming system is applied as a physical configuration, and which can prevent materials/components of an image forming apparatus from deteriorating, the image forming apparatus which only makes sheets pass through (sheet-passing) in single-sided printing.
The problems raised by the image forming systems disclosed in Japanese Patent Application Laid-open Publications No. 2005-22243 and No. hei 10-86455 are also problems for a tandem-type image forming apparatus in which two image forming units are connected in series.